That's there in response to the Americans' love of litigation. The producer of the handbook has obtained the data from the original specification sheets issued by the US Military in WWII to standardize hardware across industry.
By World War II (1939–1945), virtually all national militaries and trans-national alliances of the same (Allied Forces, Axis powers) were busy standardizing and cataloguing. The U.S. AN- cataloguing system (Army-Navy) and the British Defence Standards (DEF-STAN) provide examples. For example, due to differences in dimensional tolerances, in World War II American screws, bolts, and nuts did not fit British equipment properly and were not fully interchangeable.
National Aerospace Standards since 1941, have served as the foundation for aircraft, spacecraft, watercraft, ground vehicles, machinery, and electronics NAS parts are most well-known for state-of-the-art, high-strength, precision fasteners, electrical connectors, splices and terminations, rod end bearings, and many other types of hardware and components. Most parts are available as 3D CAD models.
MS- Military standard started around the 1950s and for the most part replaced the AN hardware series.
Quick explanation: https://www.flywithspa.com/docs/pbm/toc453317738.html